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konimarti / opc

OPC DA client in Golang for monitoring and analyzing process data based on Windows COM.

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panic: runtime error: invalid memory address or nil pointer dereference

SSSOCPaulCote opened this issue · comments

commented

I cloned the repo, and ran go test -v ./... but I keep getting this error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x0 pc=0x1015168]

Manually testing this package by trying to follow the example on the main page with a running OPC server on my PC also yields this result.

I'm running go 1.17.1 on Windows 10. Here's my test code:

package main

import (
	"fmt"
	"github.com/konimarti/opc"
)

func main() {
	c, _ := opc.NewConnection(
		"Fluke.DAQ.OPC",
		[]string{"DESKTOP-<redacted>"},
		[]string{"Instrument 01.Module 3.Channel 304"},
	)
	defer c.Close()
	fmt.Println(c.Read())
}
commented

Investigating and it might have to do with NewAutomationObject method in connection_windows.go. At line 223, you declare a pointer of type ole.IUnknown as such var unknown *ole.IUknown but maybe anytime you declare a pointer, you should do it this way var unknown *ole.IUnknown = new(ole.IUnknown) based on this article

commented 
goroutine 1 [running]:
github.com/go-ole/go-ole.(*IDispatch).VTable(...)
        C:/Users/<redacted>/go/pkg/mod/github.com/go-ole/go-ole@v1.2.4/idispatch.go:18
github.com/go-ole/go-ole.getIDsOfName(0x0, {0xc0000cf7c8, 0x1, 0x12994c40598})
        C:/Users/<redacted>/go/pkg/mod/github.com/go-ole/go-ole@v1.2.4/idispatch_windows.go:20 +0xc8
github.com/go-ole/go-ole.(*IDispatch).GetIDsOfName(...)
        C:/Users/<redacted>/go/pkg/mod/github.com/go-ole/go-ole@v1.2.4/idispatch.go:22
github.com/go-ole/go-ole.(*IDispatch).GetSingleIDOfName(0xac4ea5, {0xcea9a4, 0x9bd487})
        C:/Users/<redacted>/go/pkg/mod/github.com/go-ole/go-ole@v1.2.4/idispatch.go:47 +0x3b
github.com/go-ole/go-ole.(*IDispatch).InvokeWithOptionalArgs(0xc0000cf8b8, {0xcea9a4, 0x0}, 0x8, {0xc0000cf8a8, 0x1, 0x1})
        C:/Users/<redacted>/go/pkg/mod/github.com/go-ole/go-ole@v1.2.4/idispatch.go:63 +0x3b
github.com/go-ole/go-ole/oleutil.CallMethod(...)
        C:/Users/<redacted>/go/pkg/mod/github.com/go-ole/go-ole@v1.2.4/oleutil/oleutil.go:51
github.com/konimarti/opc.(*AutomationObject).GetOPCServers(0x0, {0xc00001a0d0, 0xc0000cf9b8})
        C:/Users/<redacted>/go/src/github.com/konimarti/opc/connection_windows.go:183 +0x88
main.listCommand(0xc0000f4160)

Or maybe it's the go-ole package that needs to fix some pointer dereferencing issue.

commented

Did you go through the Troubleshooting section? Try setting the architecture to $ENV:GOARCH="386" in Powershell and compile everything again. Most of the time, this is the issue or a wrong ProgID. Also, please add opc.Debug() before the opc.NewConnection call to print more debug-related information.

commented

@konimarti setting GOARCH to 386 worked. Thank you for responding. I'll close this issue!